EP1666724B1 - Method of maximising the energy collection of a wind turbine - Google Patents

Description

The present invention relates to a method for controlling a wind energy installation and a wind energy installation with a control device for controlling the wind energy installation.

Wind turbines with controls have been well known for years and are now being used successfully. The control system in particular has a major influence on the energy yield of a wind turbine.

As a result of the continuous further development of the wind energy plants, these have developed into complex plants in which a large number of parameters and setting values have to be coordinated with one another in order to enable optimal operation.

Due to the high complexity of the systems and the high development costs for the development or further development of such systems, considerable amounts have to be spent on the purchase of such a system. It is easy to understand that such expenditures are only acceptable if the wind turbine during its lifetime is derived from its operation allow the resulting proceeds to generate as large a surplus as possible in addition to the amortization.

However, this excess is inextricably linked to the power yield of a wind energy plant and therefore maximizing the yield has a comprehensibly high priority, in particular for the owner / operator of such a plant.

On the other hand, deviations from the ideal dimension are inevitable in all production processes and in view of the complexity of wind turbines and their dimensions. Tolerance limits determine the range within which such deviations are still considered acceptable.

Regardless of the question of whether such a deviation is actually acceptable or not, it means a loss of income in any case, since it represents a deviation from the optimal arrangement.

The document DE 19 532 409 A1 relates to a method for operating a wind energy installation and an associated wind energy installation, in which the performance of the wind energy installation is reduced as a function of the wind speed from a predeterminable wind speed by reducing the operating speed of the rotor of the wind energy installation when a wind occurs with a wind speed above a limiting wind or inflow speed. The document DE 19 934 415 A1 is an optimization device to increase the yield of wind turbines by more accurate azimuth tracking. Accordingly, an optimization strategy for increasing the yield in wind energy plants by more precise azimuth tracking is provided, in which the knowledge of an optimally adjustable angle between the rotor axis and wind direction is based on the detection and evaluation of wind direction, wind speed and generated power.

The document TANAKA T ET AL: "Output control by hill-climbing method for a small scale wind power generating system", RENEWABLE ENERGY, PERGAMON PRESS, OXFORD, GB, Vol. 12, No. 4, December 1, 1997 (1997-12- 01), pages 387-400, XP004101206, ISSN: 0960-1481, DOI: 10.1016 / S0960-1481 (97) 00055-4 describes a control method for a wind energy generation system in order to generate wind energy as effectively as possible, even if the characteristics of the system are unknown.

The object of the present invention is to develop a method and a wind energy installation of the type mentioned at the outset in such a way that yield losses, in particular as a result of deviations in the area of the conversion of the kinetic energy of the wind into electrical energy, that is to say in the area of the rotor, drive train and generator, are as small as possible are.

For this purpose, the method of the type mentioned at the outset is developed in such a way that at least one operating setting is varied within predetermined limits.

The invention is based on the knowledge that the tolerances move within known ranges and a variation of at least one operating setting such as, for. B. the blade angle, the azimuth position, the generator torque, etc. must therefore lead to the optimal setting within this tolerance range.

In order to avoid that a permanent loss of yield ultimately results in a greater loss of yield, these variations are carried out at predeterminable time intervals, so that if an optimal setting has been found, it is retained for a predetermined period of time.

In a particularly preferred embodiment of the invention, the time intervals are varied depending on predeterminable location and / or operating conditions, so that the location peculiarities, such as relatively uniform or turbulent wind flow, wind direction changes, or the like, can be taken into account.

In a particularly preferred development of the invention, the variation is carried out promptly after a change in the operating setting triggered by external influences. If the time is sufficiently short, the operating setting is varied beyond the predefined setting value and possibly a predetermined amount in the opposite direction until the optimal setting is found. This process corresponds approximately to a settling process.

In the method according to the invention, the difference between the initial setting and the varied setting with the optimum yield is particularly preferably determined and taken into account in the subsequent changes and / or variations. In this way, the variation process and thus the achievement of maximum yield can be shortened.

In a particularly preferred embodiment of the invention, a wind power installation according to the invention comprises a control device which is suitable for carrying out the method, the control device having a microprocessor or microcomputer and a storage device.

Further advantageous embodiments of the invention are specified in the subclaims.

Figur 1

eine Darstellung des Grundprinzips der vorliegenden Erfindung an Hand eines Diagrammes;

Figur 2

eine Darstellung eines verbesserten Grundprinzips ;

Figur 3

eine weiter verbesserte Variante des erfindungsgemäßen Verfahrens;

Figur 4

ein weiter optimiertes Verfahren; und

Figur 5

ein zur Ertragsmaximierung noch weiter optimiertes, erfindungsgemäßes Verfahren.

An exemplary embodiment is explained in more detail below with reference to the figures. Show:

Figure 1

a representation of the basic principle of the present invention using a diagram;

Figure 2

an illustration of an improved basic principle;

Figure 3

a further improved variant of the method according to the invention;

Figure 4

a further optimized procedure; and

Figure 5

a method according to the invention which is further optimized for maximizing yield.

In Figure 1 the basic principle of the method according to the invention for controlling a wind turbine is shown. In the figure, the time t is plotted on the abscissa, the variation of an operating setting, such as the azimuth angle (α) of the nacelle and thus the rotor of a wind turbine, is shown in the upper part of the ordinate, and in the lower part is shown in for the sake of clarity a simplified representation of the course of the yield in the form of a performance curve (P).

It can be seen from the upper characteristic curve that the variation of the operating setting from the initial position begins sinusoidally in a positive direction at time t1, has reached a maximum value at time t2 and has reached the initial value again at time t3. From there, the variation is now continued in the opposite direction, again reaching the maximum at time t4 and again assuming the initial value at time t5.

If there is an increase in yield during this variation, the operating setting can be changed accordingly, so that the wind turbine delivers a higher yield.

The lower curve shows the yield, which varies depending on the operating setting. At time t1, i.e. at the beginning of the variation, the yield decreases until the maximum of the variation is reached at time t2, and while the setting is returned to the initial value (t3), the yield increases again until it also ends at t3 Baseline reached. When the direction of variation is reversed, the yield also decreases again in the present example, reaches the minimum (the maximum of the decrease in yield) at time t4 and returns to its initial value at time t5. This clearly shows that the initial setting of the wind turbine was optimal.

At a predetermined time (in this example t6) after a predetermined interval has elapsed, the process can be repeated.

This method competes on the one hand with the possibility of an increase in yield and on the other hand with the loss in yield that occurs due to the variation of an optimal setting.

One way to reduce this loss in earnings is in Figure 2 shown. In this figure, the time is again plotted on the abscissa, while the upper characteristic curve shows the variation of the operating setting and the lower characteristic curve shows the course of the yield on the ordinate.

While the increase in the operating setting continues to be sinusoidal starting from the initial value, the edge steepness of the signal is increased after reaching the peak value, so that the return to the initial value takes place as quickly as possible. The distance between the times t1 and t2 remains compared to Figure 1 essentially unchanged; however, the distance between times t2 and t3 is significantly reduced. In the ideal case, the distance between t2 and t3 will approach zero, so that at least in a first approximation, the loss of yield in this section between times t2 and t3 will also be very small.

The same is repeated for the negative half-wave, the rise of which is again sinusoidal and takes place between the times t3 and t4, while the return to the initial setting takes place again in the period between t4 and t5 with the greatest possible steepness. Accordingly, the loss of earnings will be halved. After a predetermined interval, this process is repeated starting at time t6. Since each setting within the range of variation (the tolerance band) can be reached and evaluated with the sinusoidally increasing course of each half-wave in the variation, this embodiment reduces the yield losses due to the variation without changing the efficiency of the variation itself.

Figure 3 shows a further embodiment of the present invention, in which the yield losses are further reduced by varying the operating settings. The division of the abscissa and ordinate corresponds to that in the other figures. Here too, the variation in the operating setting begins at time t1.

In the example shown, the yield increases up to a maximum. If the amount of the variation is increased further, the yield drops again, i.e. the maximum yield and thus the optimal operating setting are exceeded. Therefore, in this method, the increase in the amount of the variation is discontinued and the setting is restored at which the maximum yield has been reached.

Here there is an "overshoot" in the upper characteristic curve, since after the yield maximum has been reached, of course, the drop in yield must first be recognized before the operating setting for the yield maximum can then be set. This already happened at time t4, so that the variation in the opposite direction no longer has to be carried out, since the maximum yield has already been found. At time t5, the variation of the operating setting begins again after a predetermined time period, the maximum amount of the variation having been reached at time t6 and until t7 the initial value is restored. Since there was a loss of yield here, the variation of the opposite direction is now carried out and at time t9 there is again a maximum yield after an overshoot at t8, so that the corresponding setting is retained.

Another embodiment of the invention is in Figure 4 shown. Here again the abscissa is the time axis and the ordinate shows the variation of the operating setting. The main change compared to the methods described above is that the direction in which the previous variation has resulted in an increase in yield is used as the starting direction for the variation.

The variation in the operating setting begins at time t1, reaches its maximum at time t2 and in turn reaches its initial value at time t3. Since there was no increase in yield in the assumed example, the variation is now carried out with the opposite sign, that is, in the opposite direction. A yield maximum is reached at time t4, and this yield maximum is maintained after a brief overshoot.

After a predetermined period of time, the operating setting is again "rotated" at time t5 and the initial direction corresponds to the direction that led to an increase in yield in the previous variation, ie the negative half-wave. At time t6, a maximum yield is again reached, so that this setting is retained. This completely eliminates the loss of earnings that would have occurred with the positive half-wave.

After a further period of time, the variation in the operating setting begins again at time t7. This in turn begins with the negative half-wave, since this in turn led to an increase in yield with the previous variation. In this case it is assumed that this is not the case, so that the maximum is reached at time t8 and the initial value is restored at time t9. Now the direction of the variation is reversed again and the negative half-wave is followed by a positive half-wave in which the yield maximum is reached at time t10, so that this value is now maintained.

Another variation begins at time t11, this time with the positive half-wave, since this led to an increase in yield in the previous variation. The maximum is reached at time t12 and the initial setting is reached again at time t13. Since a yield maximum is again reached at time t14 in this example, this setting is retained, so that the subsequent variation will begin again with the negative half-wave.

Figure 5 shows a still further improved embodiment of the present invention. In this figure, the abscissa is again the time axis, while the ordinate in the upper part shows the change in an operating setting and in the lower part the yield curve. In this embodiment of the method according to the invention, yield losses due to the variation are reduced even further. This is achieved with the method according to the invention in that the direction of variation is reversed when a loss of yield is ascertained. If, after the direction of variation is reversed, there is again a loss in yield, the variation is terminated.

In the Figure 5 the variation begins again at time t1 with a positive half-wave and at time t2 the maximum yield is reached. After an "overshoot" (t3), the maximum yield is set at time t4 and maintained for a predetermined time period until a variation begins again at time t5.

This in turn begins with a positive half wave. However, there is already a loss of income at time t6. Therefore, the direction of variation is reversed and the negative half-wave of the variation in the operating setting begins at time t7. A yield maximum is reached at time t8 and, after an overshoot (t9), this setting is retained at time t10. After a further predetermined time period, the operating setting is again varied at time t11.

Since the negative half-wave led to an increase in yield in the previous variation, this variation also begins with the negative half-wave. Already At time t12 it is recognized that this direction of variation leads to a loss of yield and the direction of variation is reversed, so that at time t13 the initial value is reached again and the positive half-wave begins.

At time t14 it is recognized that this variation direction also leads to a loss in yield, and the variation process is terminated. The output operating setting is restored at time t15.

In order to clarify the essential advantage of this embodiment, the predetermined variation limit (T) is entered in both directions from the initial setting in the figure. Due to the considerably smaller amplitude of the variation in the operating setting, the yield losses in this variation are also considerably less. The possibility of a significant increase in yield is countered by a negligible loss of income in the event that the initial operating setting is already the optimal operating setting.

In addition to the compensation of unavoidable manufacturing or assembly tolerances that this invention enables, the method proposed according to the invention can also result in an increase in yield when changing external operating conditions, such as the wind direction, if the change is still within the tolerance range of the system control. So changes e.g. the wind direction only by a small amount, then the azimuth adjustment is not activated as a result of the change in wind direction. Nevertheless, a slight change in the inflow angle results in a slight loss in yield. This can be compensated for by the method according to the invention if the azimuth setting is varied regularly.

Compensation for assembly errors is also possible. A false display of the wind vane, e.g. B. by an assembly error, can be compensated for by the control according to the invention, provided that it is within the tolerance range of the system control. As a result, a non-optimal energy yield can be optimized based on the display result of the wind vane.

The invention is preferably applicable to a set of operating parameter settings. Preferred parameters here are the pitch setting (rotor blade angle setting), the azimuth setting (rotor setting) and the excitation current of the generator for determining the generator torque.

Depending on the wind conditions, there is a parameter set for a wide variety of parameter settings, which can be stored in the form of a table for control purposes. The wind speed measured then results in an optimal high-speed number (the ratio of the peripheral speed of the rotor blade tip to the wind speed) for a maximum energy yield for the specific system type. Since, due to the known rotor parameters, the torque available at this wind speed is known, an optimal generator torque can be determined using the specifications in the table.

If the generator torque is not adapted to the high-speed number, there are disadvantages. If the generator torque is too low, the high-speed number increases and the rotor accelerates undesirably because the wind supplies a corresponding amount of energy. If the generator torque is too high, the rotor is braked too far, so that the rotor runs too slowly and does not take the maximum possible energy from the wind. However, since the generator torque is directly dependent on the level of the excitation current, there is an adjustment option in order to influence the operation of the wind power plant in this way in the sense of optimization.

A further possibility of the application according to the invention relates to the azimuth adjustment, in order to make a possible yaw angle as small as possible, and the setting of the angle of attack of the rotor blades (pitch), in order in turn to achieve a maximum torque and accordingly to withdraw a maximum of energy from the wind.

Claims (16)

1. Method for controlling a wind turbine, characterised in that at least one operational setting (a) is varied within predetermined limits (T), wherein the variation is performed in predeterminable time intervals (t1, t2, t3, t4, t5, t6, t7, t8, t9, t10) so that, when an optimal setting has been found, this is maintained for a given period of time.
2. Method according to claim 1,
   characterised in that the time intervals are varied in response to predefinable ambient and/or operating conditions.
3. Method according to one of the preceding claims,
   characterised in that the variations are by a predefined amount in one direction, starting from the initial setting, or successively in two opposing directions.
4. Method according to one of the preceding claims,
   characterised in that the variation is performed after a change in an operational setting (a) has been caused by external factors.
5. Method according to one of the preceding claims,
   characterised in that a tip speed ratio of a rotor blade is detected contemporaneously with the variation of the operational setting (a).
6. Method according to claim 5,
   characterised in that a difference between the initial setting and the varied setting with the highest tip speed ratio is quantified.
7. Method according to claim 6,
   characterised in that the quantified difference is taken into account in every subsequent change of operational setting (a) in response to external factors.
8. Method according to one of the preceding claims,
   characterised in that the rotor blade pith angle and/or the azimuth setting and/or the generator torque is varied.
9. Method according to one of the preceding claims,
   characterised in that the varied setting, the direction and the amount of variation are stored and/or analysed.
10. Method according to one of the preceding claims,
    characterised in that the amount of variation is increased with a first speed and reduced with a second speed.
11. Method according to claim 10,
    characterised in that the first speed is less than the second speed.
12. Method according to one of the preceding claims,
    characterised in that the direction of variation that led in the preceding variation phase to an increase in power yield is used as the direction for the variation.
13. Method according to one of the preceding claims,
    characterised in that the direction of variation is reversed if the power yield has decreased.
14. Method according to claim 13,
    characterised in that the variation is terminated after a power yield reduction occurs following a reversal of the direction of variation.
15. Wind turbine for performing the method according to any one of the preceding claims, wherein the wind turbine comprises a rotor, a generator connected thereto and a controller for controlling each turbine parts, for example the pitch of the rotor blades of a rotor and/or of the generator and/or for setting the attitude of the rotor to the wind.
16. Wind turbine according to claim 15,
    characterised in that the controller includes at least one microprocessor or microcontroller and a memory device.

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